Remove dependency on futures-lite

[chadaustin]

futures-lite is only used for a convenience macro and it's easy enough to inline it. This avoids pulling in futures-lite dependencies like fastrand and waker-fn, reducing the need for security updates.

Separately, tokio's net feature is not needed, so remove it.

Before:

tokio-eventfd v0.2.1 (/home/chadaustin/projects/tokio-eventfd-2)
├── futures-lite v1.13.0
│   ├── fastrand v1.9.0
│   ├── futures-core v0.3.31
│   ├── futures-io v0.3.31
│   ├── memchr v2.7.4
│   ├── parking v2.2.1
│   ├── pin-project-lite v0.2.15
│   └── waker-fn v1.2.0
├── libc v0.2.164
└── tokio v1.41.1
    ├── bytes v1.8.0
    ├── libc v0.2.164
    ├── mio v1.0.2
    │   └── libc v0.2.164
    ├── pin-project-lite v0.2.15
    ├── socket2 v0.5.7
    │   └── libc v0.2.164
    └── tokio-macros v2.4.0 (proc-macro)
        ├── proc-macro2 v1.0.89
        │   └── unicode-ident v1.0.13
        ├── quote v1.0.37
        │   └── proc-macro2 v1.0.89 (*)
        └── syn v2.0.87
            ├── proc-macro2 v1.0.89 (*)
            ├── quote v1.0.37 (*)
            └── unicode-ident v1.0.13
[dev-dependencies]
└── tokio v1.41.1 (*)

After:

tokio-eventfd v0.2.1 (/home/chadaustin/projects/tokio-eventfd)
├── libc v0.2.164
└── tokio v1.41.1
    ├── bytes v1.8.0
    ├── libc v0.2.164
    ├── mio v1.0.2
    │   └── libc v0.2.164
    ├── pin-project-lite v0.2.15
    ├── socket2 v0.5.7
    │   └── libc v0.2.164
    └── tokio-macros v2.4.0 (proc-macro)
        ├── proc-macro2 v1.0.89
        │   └── unicode-ident v1.0.13
        ├── quote v1.0.37
        │   └── proc-macro2 v1.0.89 (*)
        └── syn v2.0.87
            ├── proc-macro2 v1.0.89 (*)
            ├── quote v1.0.37 (*)
            └── unicode-ident v1.0.13
[dev-dependencies]
└── tokio v1.41.1 (*)

Fixes #3

[polachok]

I think we should switch to https://doc.rust-lang.org/stable/std/task/macro.ready.html